<span>The avian heart has evolved into a large and powerful organ with rapid muscular contractions. Generally the smaller the species the larger the relative heart size. Generally birds have hearts larger and ones that beat faster than mammals. The human heart weight amounts to .42 percent of body weight and the pulse rate at rest averages 72 beats per minute. The House Sparrow's heart constitutes 1.68 percent of the body weight and the pulse rate at rest averages 460 beats per minute. In the Ruby-throated Hummingbird these figures rise to 2.37 percent and a pulse rate of 615.</span>
The switching from lysogenic to the lytic cycle, also called lysogenic induction, can be caused by a double-stranded break in the prophage or can be caused by a mutagen. These factors could cause disruption of the cI & cro genes that are responsible for regulating the lytic-lysogenic cycles of bacteriophages..
Mucus is what makes a frog feel slippery or slimy. Frogs don't drink water, instead they absorb it through their skin. Frogs also use their skin to breathe. A layer of mucus on the skin helps keep moisture trapped next to it, and this moisture transfers oxygen into the frog's body.
